The boy, which hadn't been named yet, was found dead in the arms of his mother, Acacia, zoo officials said. Officials called his death one of the saddest events in zoo history.

Zoo officials confirmed his death around 1 a.m. Wednesday and believe Acacia may have accidentally rolled over him while sleeping. All examinations showed the newborn was healthy, the zoo's chief veterinarian said.

The baby was delivered by C-section on Sunday after Acacia had a difficult 24-hour labor period, zoo officials said. He was the third gorilla born at the zoo since August 2012.

Zoo officials reunited mom and son Tuesday as Acacia showed increased interest in the baby even as she was still recovering from surgery. This was Acacia's first birth.

A Mexican photojournalist who left the state he worked in because of threats was among five people found shot to death in a Mexico City apartment this weekend, officials and press freedom advocacy groups said.